Preparation of beryllium nitride



Patented Sept. II, 1951 s 1 "UNITED STATE PREPARATION or ,NI'TRIDE Alexander s. Langsdorf, Jr., Chicago, 111., assignor to the United States of America as representedby the United States Atomic sion EnergyCommisi No Drawing. Application June 10, 1948,

Serial No. 32.259

5 Claims. (01. 23 191 Thisinvention relates to a. process for the preparation of a nitride of beryllium and more particularly a process wherein beryllium nitride is'prepared under controlled conditions.

" An object of this invention is to provide a process -'for the preparation of beryllium nitride v(BezaNz) containing substantially the theoretical iamount'of nitrogen (50.8 weight percent) and having an optimum density and specific gravity.

-"A further object of this invention is to provide a process for the preparation of beryllium nitride wherein the reaction is carried out at a controlled rate.

Other objects and advantages will become apparent to those skilled in the art upon further examination of the specification.

- I have discovered that beryllium metal can be 'nitrided rapidly and completely by the use of hydrogen gas mixed with nitrogen in a hydrogen concentration of substantially less than 75 percent by volume. The addition of hydrogen to the nitriding system apparently exerts a catalytic action in the formation of beryllium nitride. The

use of hydrogen results in increased yield over that obtained with pure nitrogen and the product formed by the process of thisinvention is superior 'to that produced by the usual nitridation processes in that the beryllium nitride formed by the nitrogen.

In accordance with the process of this invention beryllium metal is conveniently nitrided at a controlled rate by using nitrogen mixed with a controlled concentration of hydrogen. The concentration, in terms of volume percent of hydrogen present with the nitrogen, should be substantially less than 75 percent by volume of hydrogen. Up to about 50 volume percent hydrogen admixed with nitrogen is a suitable proportion since a hydrogen concentration of more than about 50 percent hydrogen reduces the reaction rate to an excessively low value. Nitrogen mixed with somewhat lower percentages, i. e. of the order of percent by volume hydrogen, reacts with beryllium metal at a satisfactory rate, and an optimum rate can be achieved by using a mixture comprising between 2 and 6 volume percent of hydrogen in nitrogen.

In general the reaction time varies inversely with the temperature. The reaction takes place suitably at temperatures elevated not in excess of the melting point of the charge undergoing the reaction and proceeds at an optimum'rate at ,process. of this invention contains substantially Q'the theoretical (about 50.8) percent by weight of invention as previously outlined; These pellets,

.which have a diameter of. about 1.29", swell about between 700 C. and 1400" G. Between these latter temperatures, the reaction is completed within about four hours. It-will-be. apparent to thoseskilled in the art that the reaction time can be further substantially decreased by increasing the pressure of the'gaseous reactants.

In accordance with the process of this invention, the reaction is suitably carried out ina.

sillimanite tube into which the nitrogen-hydrogen mixture flows in one end and the hydrogen and excess nitrogen flow from the opposite end,

passing out through a throttling valve and bubbler.

In the process of this invention. it is preferred to use beryllium metal in a form-such as chips to provide. additional surface area for reaction with the gaseous nitrogen-hydrogen mixture.

In a furtherrembodiment. of this invention an alloy of beryllium'containing :a small amount,

i. e. about 3 percent, of an element suchas aluminum, which promotes nitridation, reacts at an .=.optimum rate with a mixture of nitrogen containing 3 percent by volume hydrogen. -The beryllium ,nitride formed thereby contains. between'47 and 49 percent by weight nitrogen and "can be further reacted by reducingit to a finelydivided state, i. e. to between 40 and mesh,

fby' grinding in .a beryllium mortarand pestle,

pressing into pellets and refiring in the same apparatus andv according to the process of this 0.005" on refiring. Their final density is about 1.77 and the nitrogen content approaches the theoretical value (50.8 weight percent). The pelleted product is strong, very hard, and quite stable in-air. In moist air, there is slow decomposition with the expected production of ammonia; however, the product keeps well in a. desiccator. The pellets are readily soluble in concentrated sodium hydroxide but dissolve somewhat more slowly in hot concentrated acid.

Example Three hundred to four hundred grams of beryllium nitride containing about 47 to 49 percent by weight nitrogen were prepared by the process of this invention in a sillimanite reaction tube measuring 1.75" inside diameter by 36" in length, 23" hot length. Beryllium chips were placed in a boat made by splitting a smaller sillimanite tube in half lengthwise. This boat was line with a thin layer of beryllia to facilitate the removal of the reaction product. The beryllium 3 chips were turned from an alloy of beryllium containing 3 percent by weight aluminum. Tank nitrogen was mixed with 3 percent by volume hydrogen and passed through the reaction tube at a rate sumcient to maintain the amount of hydrogen present between 3 and 5 percent. The system was heated for about one hour until the reaction began at 870 C. and heating at about 1150 C. was continued for about four hours. Cooling from a final temperature of 1250 C. required twelve hours, bringing the total reaction time between seventeen and eighteen hours.

The nitride was then ground to 60 mesh in. a. mortar and pestle made from a berylliumalloy containing 3 percent aluminum and this ground nitride was then pressed into pellets in a demountable die. These pellets were then reflred in contact with the gaseous nitrogen mixed with 3 percent hydrogen in the same sillimanite furnace at a temperature of about 1200 to 1300" C.

Theabrasive character of the product is illusstrated by the fact that on pressing pellets measuring between 1.25" by 1.50" at 60 tons pressure, about 0.0001" is worn from the die wall each time a pellet is pressed.

The process of this invention can be adapted to production on a commercial scale by using a vertical gas-tight globar heated furnace. The lowdensity briquettes of beryllium alloy, measuring about 3.25" in diameter and about 3" high, have a hole drilled through the axis to furnish greater surtace area for contact with the gaseou reactant mixture. The furnace is sealed and flushed thoroughly with nitrogen containing 3 percent hydrogen until the reaction rate is increased sufllciently to maintain the reaction without further appreciable electric heating.-

From about 12 lbs. of'the briquettes made from the beryllium-aluminum alloy, about 23 lbs. of beryllium nitride containing at least about 46 percent by weight nitrogen are produced within 18 hours. This beryllium nitride is crushed in a power-operated jaw-crusher to a size sui'ficient to pass a 40- to GO-m'esh screen and is formed into pellets having a specific gravity of about 1.7 and subjected to further nitriding at about 1300* C. in the globar furnace. The beryllium nitride pellets increased both in dimensions and a predetermined size. Obviously the change in size on refiring will be less if, prior to reflring, the nitride material contains close to the theoretical weight of nitrogen.

The foregoing descriptions comprise the preferred embodiments of this invention. However, many alterations and changes may be made therein without departing from the spirit and scope of this invention as set forth in the appended claims which are intended to cover, as broadly as possible in view of the prior art, all features of novelty, either singly and/or in combination.

What is claimed is:

1. A process for the preparation of beryllium nitride comprising heating beryllium metal in contact with a mixture consisting of nitrogen and hydrogen wherein the concentration of hydrogen is between 2 and 6 percent by volume hydrogen.

2. The process of claim 1 wherein the temperature of the reaction is between '700 and 1400 C.

3. The process of claim 2 wherein the metal reactant is in a fine state of sub-division.

4. A process for the preparation of beryllium nitride containing nitrogen in an amount substantially identical with the amount of nitrogen present in the compound of the formula BeaNz and having an increased density, comprising pressing a pulverized and partially nitridedberyllium into pellets and retiring said pelleted and nitrided' beryllium at 1200 to 1300 C. in contact with nitrogen containing about 2 to- 6 percent by volume hydrogen.

5. A process for the preparation of beryllium nitride comprising heating a beryllium alloy consisting of beryllium and about 3 percent by weight aluminum at a temperature of about 1200* C. with a binary gaseous mixture consisting of nitrogen and between 2 and 6 percent by volume hydrogen gas.

ALEXANDER S. LANGSDORF, Ja.

REFERENCES CITED The following references are of record in the file of this patent:

Fichter et al., Zeitschrift fur anorganische und allgemeine Chemic, vol. 93, page 88 (1915).

Satoh, Nature, vol. 133, page 837 (1934) Mellor, Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 8, page 153 (1928). 

1. A PROCESS FOR THE PREPARATION OF BERYLLIUM NITRIDE COMPRISING HEATING BERYLLIUM METAL IN CONTACT WITH A MIXTURE CONSISTING OF NITROGEN AND HYDROGEN WHEREIN THE CONCENTRATION OF HYDROGEN IS BETWEEN 2 AND 6 PERCENT BY VOLUME HYDROGEN. 